EVOLUTION OF BENTHIC ANIMAL BEHAVIOR IN THE DEEP SEA AS REFLECTED IN THE GRAPHOGLYPID TRACE FOSSIL RECORD

The deep sea trace fossil record is exemplified by graphoglyptids, which are highly organized, geometically patterned, horizontal burrows often found preserved as sole casts in positive relief on the base of turbidites. Some previous workers have suggested that the graphoglyptid trace makers were slowly diversifying through geologic time, becoming optimized for efficient feeding and getting smaller over time until the Late Cretaceous, when a sudden increase in diversification occurred. Detailed geometric analyses of over 400 graphoglyptid specimens, ranging in age from Cambrian to the present, reveal that different morphologic categories of graphoglyptids (e.g., regularly meandering and mesh-shaped burrow networks) represent organisms’ responses to evolutionary pressures in unique ways. It is apparent that the times of significant evolutionary changes in behavior were not consistent among various morphological groups of benthic feeding patterns. It is likely that the behavioral evolution of graphoglyptid burrowers was influenced by global influences on the deep marine environment, such as climate change, glaciation, and deep-ocean warming during the Late Cretaceous, Eocene, and Oligocene. The global influences affected each morphological group of graphoglyptids uniquely, suggesting that each of the topologic categories was created by different species or genera of trace maker.